Total Synthesis of (+)-Paucidactine D

Area of Science:

• Organic Chemistry
• Natural Product Synthesis
• Medicinal Chemistry

Background:

• (+)-Paucidactine D is a complex natural product with potential biological activity.
• The synthesis of such intricate molecules presents significant challenges in organic chemistry.
• Previous studies have established a common intermediate for synthesizing various alkaloid classes.

Purpose of the Study:

• To detail the first total synthesis of (+)-paucidactine D.
• To showcase a novel synthetic strategy utilizing bridging cyclizations.
• To demonstrate the versatility of a common intermediate for divergent alkaloid synthesis.

Main Methods:

• A SmI2-mediated intramolecular C21-C2 free radical cyclization to form a bicyclo[2.2.2]octane core.
• An intramolecular SN2 displacement reaction to form a bridging lactone ring.
• A [4+2]/[3+2] cycloaddition cascade of 1,3,4-oxadiazole to assemble the pentacyclic Aspidosperma skeleton.

Main Results:

• Successful total synthesis of (+)-paucidactine D (4) from pentacyclic intermediate 13.
• Construction of a highly substituted bicyclo[2.2.2]octane core and a bridging lactone.
• Efficient assembly of the Aspidosperma skeleton via a cycloaddition cascade, yielding a single diastereomer.

Conclusions:

• This work provides the first total synthesis of (+)-paucidactine D.
• The developed synthetic strategy highlights efficient methods for constructing complex alkaloid frameworks.
• The study reinforces the utility of intermediate 13 for the divergent synthesis of eight distinct alkaloid classes.